Nepomniachtchi's preparation probably ended around here. With a pawn for the exchange and still all the plusses mentioned earlier. White has the advantage.
18... f6d5  19. h1d1 [%c_effect d1;square;d1;type;GreatFind;persistent;true] Another important move to protect the d4-knight and make the e3-e4 advance available in case the poor piece on a2 tries to run away. 19... d5b4  20. g2b7  20... a8a7 